To go get beer or other alcohol. Used chiefly in the coal region of northeast Pennsylvania. Derived from old coal mining days, when the miners would take a growler (a type of metal bucket) and put their lunch in it, and put their coffee in the bottom in a separate compartment. This was supposedly to keep the meal warm, but it probably didn't work too well. On the way home from work, the miner would "rush the growler" over to the local watering hole and fill it up with cans or bottles of beer to bring home. Hence, rush the growler.